1. Field of the Invention
The present invention relates to a method of manufacturing a tantalum condenser, and more particularly, to a method of manufacturing a tantalum condenser, in which a high-performing tantalum condenser is manufactured through a more simplified and higher-efficient process using simpler and economical equipment.
2. Description of the Related Art
A tantalum condenser utilizes tantalum Ta as an electrode. That is, tantalum is a conductor but turned into a high-quality insulator when oxidized. When it comes to a tantalum condenser, the tantalum is oxidized as an anode into dielectrics and then an additional cathode is formed. The tantalum condenser is obtained by utilizing pores generated when tantalum powder is sintered and hardened.
There are two types of tantalum condensers. One is a wet tantalum condenser which employs an electrolyte solution and has a silver Ag case formed at a cathode to prevent the electrolyte solution from leaking. The other one is a dry tantalum condenser which uses a solid such as manganese dioxide as an electrolyte without adopting the electrolyte solution.
FIG. 1 is a flow chart illustrating a conventional method of manufacturing a tantalum condenser. To manufacture the tantalum condenser, first, a tantalum powder is sintered to form a pellet as in operation S10. Then, the tantalum pellet formed is oxidized and chemically reformed to have an oxide formed on a surface thereof as in operation S12.
When the oxide, i.e., dielectric layer is formed on the surface of the tantalum pellet, a cathode layer is formed. A polymer layer is formed as the cathode layer in operation S14. Generally, the polymer layer is immersed in a solution containing monomors and the monomers are polymerized on the surface of the tantalum pellet, i.e., in pores. After the polymer layer is formed, the tantalum pellet is chemically reformed to cover defects of the dielectric layer in operation S16. To be chemically reformed, the tantalum pellet is immersed in a chemical reformation solution while a voltage is applied.
With the chemical reformation completed, the tantalum pellet is cleaned to remove the residual chemical reformation solution which may act as impurities to adversely affect the product in operation S18. After the cleaning, it is checked whether the cathode layer has been fully formed in operation S19. In a case where the polymer layer, i.e., cathode layer is not completely formed as in S19: N, the polymer layer is formed again on the tantalum pellet as in operation S14, and then tantalum pellet is chemically reformed and cleaned as in operations S16 and S18. With the cathode layer completely formed in operation S19: Y, the tantalum condenser is manufactured
FIG. 2 illustrates a tantalum pellet immersed in a chemical reformation solution in manufacturing a tantalum condenser according to a conventional method. The tantalum pellet 20 is immersed in a chemical reformation bath 23 while being connected to a metal plate 21. The tantalum pellet 20 has a dielectric layer and a polymer layer formed on a surface thereof. The chemical reformation solution 22 may utilize an acidic solution, for example, an acidic aqueous solution such as phosphoric acid, sulfuric acid, nitric acid, acetic acid, ammonium nitrate, and sodium nitrate. Alternatively, the chemical reformation solution 22 may adopt an aqueous solution containing a dopant such as p-TSA.
Chemical reformation is performed by connecting power 24 to the tantalum pellet 20 and the chemical reformation solution 22 and applying voltages. Here, a positive (+) voltage is applied to the tantalum pellet 20 which is an anode and a negative (−) voltage is applied to the chemical reformation solution 22.
This chemical reformation necessarily should be followed by a cleaning process for removing the residual chemical reformation solution. In a case where the chemical reformation solution is p-toluene sulfonic acid (p-TSA), the tantalum pellet needs to be cleaned with water to remove the p-TSA. An electrolyte of this chemical reformation solution and a cleaning material remaining in the polymer layer, i.e. cathode layer causes current to leak from the cathode layer, thereby adversely affecting performance of the condenser.
The cleaning after chemical reformation is typically carried out in a solution having a high temperature of 50 to 80° C. At this time, the cleaning after chemical reformation may be performed even though the polymer layer is formed outside the tantalum pellet. This however causes the polymer layer to be detached from the pellet or generates cracks on the polymer layer itself. Also, such cleaning after chemical reformation requires additional cleaning and drying equipment.
That is, after chemical reformation, the chemical reformation solution should be cleaned by way of at least one cleaning and drying process. Consequently, the chemical reformation and the cleaning thereafter trigger unnecessary stress and destabilize an overall system, thereby degrading process efficiency and posing a difficulty to quality management.
Therefore, there have been continued demands for a method of manufacturing a tantalum condenser in a more simplified and economical fashion while maintaining or increasing performance of the tantalum condenser.